Equipment for moving materials is known in the art which is made up from modular frames carrying a coplanar array of parallel, motor-driven rollers on which a pallet loaded with material to be transported, resting on the rollers, is conveyed along a predetermined course formed by a plurality of modules located adjacent each other, in end-to-end alignment.
Such equipment has considerable limitations in use as the roller frames are effective only for forming straight, horizontal courses; auxiliary equipment such as lifts, chutes and turntables are thus required for forming courses with changes in height or direction.
Other known conveyors are so-called "rolling-shutter" conveyors in which one or more endless roller chains which pass over two end pulleys are guided along a metal support structure having the shape, in plan, of the course to be travelled; flat support elements are connected to the chains and located adjacent each other so as to form a substantially continuous, articulated support bed like that defined by a rolling shutter for a window; the objects to be conveyed may be placed on this bed either directly or on pallets. These conveyors are very bulky, are very expensive to install and maintain, are not very reliable because of the long length of the drive chains, which is twice that of the course actually covered by the conveyor, which causes problems in maintaining the tension in the chains, of seizure of the rollers forming the chains and noise.
Similar problems are presented by ground-based conveyors in which the load is carried on platforms mounted on carriages driven along guides of a metal support structure by one or more motor-driven chains of the type previously described through rigid mechanical transmission devices, which may be deactivatable temporarily, for example to form accumulations.
Finally, overhead conveyor systems are known which are constituted by a suspended guide along which motor-driven carriages are movable, for example on wheels, and from which conveyor hooks are suspended; the carriages pick up control signals and power for their motors directly from conductive tracks (bus bars) carried by the guide through sliding shoes. Such systems are very efficient and silent but are suitable only for very clean working environments as, otherwise, the conductive tracks quickly become soiled by dust, grease, etc, causing loss of contact between the tracks and the shoes of the carriages with the possible loss of control and/or power at least along certain sections. Moreover, it is not possible to use such conveyors in inflammable environments since the rubbing of the shoes on the bus bars may cause sparks. Finally, these conveyors, if also used on long inclined courses (either rising or descending) are suitable only for limited loads since, beyond certain loads, the wheels may slide on the guides.
The aforedescribed drawbacks may be partly overcome by the conveyor system according to U.S. Pat. No. 5,062,368. However, this reference relate to a conveyor system primarily adapted to be used solely on the ground and that, in any case, needs, to be operated effectively, to be built with a very high precision, specially as far as the guides and the engagement system of the pallet are concerned. This leads to very high production and maintenance costs. Moreover, this system is suitable for pallets of small dimension only and can displace the pallet along orthogonal directions only. Finally, at least as least far as the embodiments shown are concerned, it does not meet, nowadays, the governmental safety regulations.